In current networks, traffic of mobile terminals (smartphones and feature phones) accounts for most of network resources. In addition, traffic used by the mobile terminals tends to increase continuously.
Meanwhile, with the development of Internet of things (IoT) services (for example, transportation systems, smart meters, and monitoring systems for devices and the like), there is a demand to cope with services that have various requirements. Therefore, in the communication standards of the fifth generation mobile communication (5G or new radio (NR)), technologies that realize a higher data rate, a larger capacity, and a lower delay are desired, in addition to the standard technologies of the fourth generation mobile communication (4G) (for example, see Non Patent Documents 1 to 11). As for the 5G communication standards, working groups of the 3GPP (for example, TSG-RAN WG1, TSG-RAN WG2, and the like) have been examining technologies (Non Patent Documents 12 to 39). The first version of the 5G standard specifications defined by the 3GPP has been released.
As described above, to cope with a wide variety of services, in the 5G, a large number of use cases that are classified into an enhanced mobile broadband (eMBB), a massive machine type communications (MTC), and a ultra-reliable and low latency communication (URLLC) are supposed to be supported.
In the wireless network, it is necessary to allocate a wireless resource to allow a terminal device to transmit data. Therefore, the terminal device performs a scheduling request procedure with respect to a base station device to which the terminal device is connected. When a physical uplink control channel (PUCCH) resource is allocated to transmit a scheduling request (SR), the terminal device transmits the SR using the PUCCH resource. In other words, a PUCCH is used as a transmission channel for the SR.
The base station device that has received the SR provides an UL grant (uplink transmission permission) for uplink transmission performed by the terminal device. When the terminal device receives the UL grant, the terminal device reports an amount of data stored in a data buffer to the base station device. This report may be referred to as a buffer status report (BSR). The base station device that has received the BSR recognizes the amount of data stored in the data buffer of the terminal device, allocates an appropriate amount of an uplink wireless resource to the terminal device, and transmits an UL grant indicating the wireless resource to the terminal device. Consequently, the terminal device transmits uplink data to the base station device using the notified wireless resource. The above-described procedure may be referred to as an SR PUCCH.
In contrast, when the PUCCH resource is not enough, the base station device does not allocate a PUCCH resource for the SR to the terminal device in some cases. In this case, the terminal device needs to perform a random access (RA) procedure in order to transmit uplink data. In the RA procedure, four signals are transmitted and received between the terminal device and the base station device. Specifically, messages as described below are transmitted and received.
Msg1 (from the terminal device to the base station device): including a random access preamble. A random access channel (RACH) is used as a channel.
Msg2 (from the base station device to the terminal device): including a random access response. A physical downlink shared channel (PDSCH) is used as a channel. Information to be transmitted includes identification information on the random access preamble in Msg1 received by the base station device and an UL grant for a message to be transmitted on the next using uplink channel.
Msg3 (from the terminal device to the base station device): a physical uplink shared channel (PUSCH) is used as a channel. A wireless resource for transmitting Msg3 is notified by the UL grant of Msg2. Further, an identifier of the terminal device is transmitted by Msg3. As a result, the base station device that receives Msg3 is able to identify the terminal device that is performing the RA procedure.
Msg4 (from the base station device to the terminal device): including an UL grant. The terminal device that receives the UL grant determines that the RA procedure is successful.
If the RA procedure is successful similarly to the SR PUCCH, the terminal device transmits a BSR using the UL grant of Msg4, receives an UL grant for allocating an appropriate amount of an uplink wireless resource from the base station device, and transmits uplink data. The above-described procedure may be referred to as an SR RACH.
As a procedure for cancelling the SR RACH, a study is being conducted to cancel the above-described procedure when an UL grant is allocated to a cell-radio network temporary identifier (C-RNTI) and when a media access control (MAC) protocol data unit (PDU) transmitted by the PUSCH includes a BSR that reflects the latest buffer status (data storing status) of the terminal device (Non Patent Documents 21 and 39).    [Non Patent Document 1] 3GPP TS 36.211 V15.1.0 (2018-03)    [Non Patent Document 2] 3GPP TS 36.212 V15.1.0 (2018-03)    [Non Patent Document 3] 3GPP TS 36.213 V15.1.0 (2018-03)    [Non Patent Document 4] 3GPP TS 36.300 V15.1.0 (2018-03)    [Non Patent Document 5] 3GPP TS 36.321 V15.1.0 (2018-03)    [Non Patent Document 6] 3GPP TS 36.322 V15.0.1 (2018-04)    [Non Patent Document 7] 3GPP TS 36.323 V14.5.0 (2017-12)    [Non Patent Document 8] 3GPP TS 36.331 V15.1.0 (2018-03)    [Non Patent Document 9] 3GPP TS 36.413 V15.1.0 (2018-03)    [Non Patent Document 10] 3GPP TS 36.423 V15.1.0 (2018-03)    [Non Patent Document 11] 3GPP TS 36.425 V14.1.0 (2018-03)    [Non Patent Document 12] 3GPP TS 37.340 V15.1.0 (2018-03)    [Non Patent Document 13] 3GPP TS 38.201 V15.0.0 (2017-12)    [Non Patent Document 14] 3GPP TS 38.202 V15.1.0 (2018-03)    [Non Patent Document 15] 3GPP TS 38.211 V15.1.0 (2018-03)    [Non Patent Document 16] 3GPP TS 38.212 V15.1.1 (2018-04)    [Non Patent Document 17] 3GPP TS 38.213 V15.1.0 (2018-03)    [Non Patent Document 18] 3GPP TS 38.214 V15.1.0 (2018-03)    [Non Patent Document 19] 3GPP TS 38.215 V15.1.0 (2018-03)    [Non Patent Document 20] 3GPP TS 38.300 V15.1.0 (2018-03)    [Non Patent Document 21] 3GPP TS 38.321 V15.1.0 (2018-03)    [Non Patent Document 22] 3GPP TS 38.322 V15.1.0 (2018-03)    [Non Patent Document 23] 3GPP TS 38.323 V15.1.0 (2018-03)    [Non Patent Document 24] 3GPP TS 38.331 V15.1.0 (2018-03)    [Non Patent Document 25] 3GPP TS 38.401 V15.1.0 (2018-03)    [Non Patent Document 26] 3GPP TS 38.410 V0.8.0 (2018-03)    [Non Patent Document 27] 3GPP TS 38.413 V0.7.0 (2018-03)    [Non Patent Document 28] 3GPP TS 38.420 V0.7.0 (2018-03)    [Non Patent Document 29] 3GPP TS 38.423 V0.7.0 (2018-03)    [Non Patent Document 30] 3GPP TS 38.470 V15.1.0 (2018-03)    [Non Patent Document 31] 3GPP TS 38.473 V15.1.1 (2018-04)    [Non Patent Document 32] 3GPP TR 38.801 V14.0.0 (2017-03)    [Non Patent Document 33] 3GPP TR 38.802 V14.2.0 (2017-09)    [Non Patent Document 34] 3GPP TR 38.803 V14.2.0 (2017-09)    [Non Patent Document 35] 3GPP TR 38.804 V14.0.0 (2017-03)    [Non Patent Document 36] 3GPP TR 38.900 V14.3.1 (2017-07)    [Non Patent Document 37] 3GPP TR 38.912 V14.1.0 (2017-06)    [Non Patent Document 38] 3GPP TR 38.913 V14.3.0 (2017-06)    [Non Patent Document 39] R2-1804572, “Miscellaneous corrections”, 3GPP TSG RAN WG2 Meeting #101bis, Sanya, China, 16-20 Apr. 2018
However, in the currently-examined procedure of cancelling the SR RACH, there is a problem in that, in some cases, it is uncertain whether cancellation is to be performed. Specifically, in certain scheduling in which a periodic wireless resource is allocated like in semi-persistent scheduling (SPS) in long term evolution-advanced (LTE-A) for example, the terminal device may be able to transmit a BSR even without receiving an UL grant from the base station device. In other words, in some cases, the terminal device may transmit a BSR using an uplink wireless resource that has been allocated in advance. In this case, the UL grant is not used to transmit the BSR, so that the SR RACH is not cancelled. Therefore, even though the BSR is already transmitted, the SR RACH procedure for transmitting a BSR is continued and an unnecessary process is performed.